ok.. then i'll walk you through it... in test-plan fashion
(it's been posted numerous times.. but i guess search has never worked on the forums...)

put on your DNP: W
then press keys in this fashion:

shift down
W down
shift up
W up

what do you think will be sent to the other wows?

shift down
W down ... since this is not W, but shift+W, it will pass
shift up

that's it. why? because the W is on the DNP therefore W up will not be passed

why do you get run-aways? due to blizzards movement model. down means go.. up means stop. no up... no stop.

btw.. 'strict' is not new. that is what i call the 'old' way of doing the dnp.
unchecking it will avoid runaways for those unaware of the dynamics. do i like it? no.. but then again, i don't get run-aways